Effect of mechanical grinding on the reaction pathway and kinetics of the thermal decomposition of hydromagnesite

Effect of mechanical grinding of hydromagnesite on the reaction pathway and kinetic behaviors of the thermal decomposition process was investigated by means of thermoanalytical techniques, together with crystallographic and morphological measurements. A crystalline hydromagnesite, the as-received sample, was decomposed in two distinguished mass loss steps of overlapped dehydration-dehydroxylation and dehydroxylation-decarbonation via an amorphous intermediate of carbonate compound. Thermal decomposition of an amorphous hydromagnesite, obtained by mechanical grinding of the as-received sample, was characterized by three well-separated decomposition processes of dehydration, dehydroxylation and decarbonation. The kinetic behaviors of the respective decomposition steps were estimated separately using a mathematical deconvolution of the partially overlapped reaction steps. From the formal kinetic analyses of the respective reaction processes, it was revealed that the dehydration and dehydroxylation processes indicate the decelerate rate behaviors controlled by diffusion, while the rate behavior of nucleation limited type is predominant for the decarbonation process.